1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, and in particular, relates to a technology which is effectively applied to a semiconductor device having a resistive field plate formed on a semiconductor substrate via an insulating film and to a method of manufacturing the semiconductor device.
2. Description of the Background Art
A power device is utilized in many fields such as, apart from a motor control inverter, a power source application for an FPD (Flat Panel Display), such as a high capacity PDP (Plasma Display Panel) or a liquid crystal panel, and a home inverter for an air conditioner or lighting. As this kind of power device, an IGBT (Insulated Gate Bipolar Transistor) or a power MOSFET is known.
Heretofore, the drive and control of the power device has been carried out by an electronic circuit configured by combining a semiconductor element such as a photocoupler and an electronic part such as a transformer. However, in recent years, owing to the advancement of LSI (Large-Scale Integration) technology, a high voltage IC(Integrated Circuit) with a breakdown voltage level of 100V to 1200V, which is used in consumer power supplies of AC100V and 200V, an industrial power supply of AC400V, and the like, has been put to practical use.
In the high voltage IC, it is often the case that a breakdown voltage structure (a structure of a portion in charge of breakdown voltage) portion includes a capacitive field plate (MFFP) or resistive field plate (RFP) formed of a high-resistance polysilicon thin film. The capacitive field plate or the resistive field plate is such that as it has the function of relaxing the electric field concentration on a depletion layer of a semiconductor surface, it is possible to stably secure a high breakdown voltage.
This kind of field plate is formed on a semiconductor layer via an insulating film, but an example of providing undulations in the semiconductor layer or insulating film under the field plate in order to further enhance the effect of electric field relaxation, is reported. For example, in JP-A-8-32031, the insulating film is made larger in thickness in the outer side portion of a spiral field plate than in the inner side portion. Also, in JP-A-2013-187240, grooves are formed in the semiconductor layer small ineffective thickness, and the insulating film and the field plate are formed so as to fill the grooves. In both JP-A-8-32031 and JP-A-2013-187240, the boundaries of the undulations are formed so as to be parallel to the field plate.
However, in the breakdown voltage structure of the high voltage IC, as a leak current when a high voltage is applied is generated in only a junction region when the capacitive field plate is provided, the leak current is as very small as several nA to several μA or less, but the enforceability of a potential on a depletion layer of the front surface of the semiconductor layer is low, and reliability is low compared with in the resistive field plate.
Meanwhile, when the resistive field plate is provided, the enforceability of a potential on the depletion layer of the front surface of the semiconductor layer is high, and reliability is comparatively high, but the leak current when a high voltage is applied is as large as several μA to several ten μA compared with in the capacitive field plate. That the leak current is large means that a leak current from a high voltage terminal to a ground terminal is large in a high voltage IC, and that the power consumption of the IC increases.
Consequently, when using the resistive field plate in the breakdown voltage structure, it is required, in order to reduce the power consumption when the IC is on standby, to increase the total resistance value of the resistive field plate and reduce the leak current.
Therefore, the present inventors have contrived the invention focusing attention on the shape of a thin film resistance layer (a resistive thin film layer) used as the resistive field plate.